XFOR: All Messages Sent Over IMC Result in NDRs

When you use the Microsoft Exchange Internet Mail Connector (IMC) to send SMTP mail the IMC may try to send messages to itself. When this happens, users will receive non-delivery reports (NDRs).

The following is an NDR that a user might receive: This problem occurs if the IMC is using DNS for the host name resolution. When the IMC attempts to resolve a host, it will attempt to query the DNS server for the host's IP address. If a site uses an MX wildcard record, it will direct all mail to that site. This could mean that the IMC will try to send mail to it's own IP address. The following scenario could help explain this:

The computer running the IMC is located in the a.com domain and there's an MX wildcard record of *.a.com in the DNS.

The IMC will add a.com to any address except ones ending in a.com. Any address that ends in a.com will use the address expressed through the MX wildcard record.

Since every address the Microsoft Exchange Message Transfer Agent (MTA) tries to resolve will end in a.com, all mail will go to the same Microsoft Exchange Server. This may be the Microsoft Exchange Server that the IMC is running on.

If you are experiencing this problem with the IMC, you can add a registry value to prevent it. The registry key is:

From the Registry Editor menu, click on Edit, then the Add Value option from there.

This is case sensitive and should be typed exactly as show above. You will need to restart the IMC for the registry key to take effect. Then you can use Restest.exe to see if it worked. This utility can be found on the Microsoft Exchange Server CD-ROM in the Support\Utils\I386 directory.